Electric thermocontact



Jan. 27, 1959 a. K. BRUNBERG ETAL 2,87

ELECTRIC THERMOCONTACT Filed Oct. 21, 1953 T1 Fig.4

k IN vz/vram Gu/wwm Amw. Elva/vain Halve Kam- 0/5750,

Unite States Patent ELECTRIC THERMOCONTACT Gunnar Karl llrunberg, Segeltorp, and Arne Kurt Dietsch, .Enslrcde, weden, assignors to Telefonaktiebolaget L M Ericsson, Stockholm, Sweden, a corporation of Sweden Application October 21, 1953, Serial No. 387,383

Claims priority, application Sweden October 29, 1952 9 Claims. (Cl. 179-184) This invention relates to a thermocontact, which is actuated by means of electric current. The contact is actuated swiftly by means of heating. However it does not return to its initial position after cooling but remains in actuated position thus causing a registration. It differs from previously known thermocontacts by its construction and by its availability. The construction is simple and involves a little need of space and small costs. It may be used both for release or break of processes and for registration and recording of a function.

This is achieved by means of a contact spring provided with a contact protruding from the spring, which contact by the spring is pressed against a point on one side of a blade of semi-conducting material, which after a certain heating easily falls to pieces, and by means of a metallic support, against which the other side of the blade is resting and which on said point is provided with a hole that corresponds to the contact and due to the fact that the contact is pressed down in said hole by the contact spring, when an electric current of sufficient strength for producing said heating passes through the contact spring, the blade and the support.

The invention will he described more closely in connection with the annexed drawings, Figs. l4.

Fig. 1 shows the principle for a registering device having a large number of thermocontacts according to the invention.

Figs. 23 show single thermocontacts for special purposes.

Fig. 4 illustrates a particularly suitable application of the invention.

In Fig. 1 there is a bar shaped member 4 of insulating material, in which a number of compressed spiral contact springs 1 are fastened. Each contact spring has a soldering ear 1c and a contact point 1a. The sides of the contact point are coated with insulating material 1b but its face end is blank and makes contact with a blade 2 of semi-conducting material. The blade 2 is pressed by the springs 1 against a support 3, which is provided with holes 3a, one hole being in alignment with each contact point la. The support 3 is shaped as a casing, which is screwed to the bar 4 and protects the springs 1. In the bar 4 there is an auxiliary pin 31), which comes into conducting contact with the casing 3, when the bar and the casing are assembled. The semi-conducting material of the blade 2 is moreover of such a kind that at a certain heating it is so damaged or altered that it easily falls to pieces. The blade 2 is common for all springs 1 and is so shaped or marked, that the resting point of each spring is determined in advance, before the blade is put into the casing 3 and this is put on.

Circuits may then be closed by the contact springs 1, the blade 2 and the support 3. If a sufficiently high voltage is applied between e. g. the terminals and 3b, the blade 2 is heated above the hole 3a, and weakened to such an extent that the contact 1a passes through the blade 2, whereby the current is broken by the insulating layer lb on the contact 1a. The thermocontact farthest to the left on the drawing is shown in actuated position.

In Fig. 2 the contact spring 1 is a leaf spring. Its contact 1a protrudes perpendicularly from the spring and is pressed against the blade 2, which covers the hole 3a in the support 3. The lower part of the contact 1a is on the sides coated with an insulating material 1b. Beneath the support 3 there is arranged a metal spring 5. The contact spring 1, the support 2 and the metal spring 5 are fastened in an insulator 4. The thermocontact is intended to be an excess-voltage arrester and is normally traversed by a weak current, which is not able to heat the blade 2 to a temperature at which the same collapses. A lasting and essential voltage increase causes that the blade 2 is destroyed and the contact In is pressed through the hole 312 against the spring 5, which is supposed to be connected to an alarm device.

The thermoccntact according to Fig. 3 is intended to act as a release arrangement. A spring 6 presses against the contact spring I, which in its turn presses its contact in against the blade 2 and the support 3. The spring 6 releases a function, e. g. break of an electric contact or release of a mechanical stop, when the blade 2 breaks. The release is produced by a current impulse through the contact spring It, the blade 2 and the support 3.

Fig. 4 is a circuit diagram according to the invention for control of connecting apparatuses within automatic telephone plants. In the figure, A is a telephone instrument within a group of telephone instruments and Sl-Sn a number of line-finders with pertaining relay sets Ni--Nn. At calls the apparatus A is connected to one of the relay sets NlNn by means of one of the line-finders Sl-Sn. To each relay set Nl-Nn there pertains a therinocontact T1Tn of the kind shown in Fig. i. As soon as the relay set, e. g. N1, is being used, a circuit will be closed through the thermocontact Tl, which burns a hole in the blade B. If the line-finders S1-Sn are controlled every day, the blade B is changed every day and each blade shall then show a perforation at each contact point. If there is no perforation there will be reason to assume that the corresponding linefinder because of some fault has been out of traflic. The blades may be made of paper pulp mixed with pulverized charcoal. The side of the blades, which is turned towards the support, is suitably metallized.

We claim:

1. A thermocontact device comprising a contact spring mounting a contact element, an electric conductor disposed opposite said contact element, and a semi-conducting member interposed between one side of said conductor and said contact element in conductive contact with the conductor and the contact element, the material of said semiconducting member having a materially reduced breaking strength when heated, said spring being biased to press said contact element against the semiconducting member, said conductor having an aperture in alignment with the direction of pressure by the con tact element upon the semi-conducting member and said spring, semi-conducting member and conductor constituting a circuit connection connectable to a source of current, a flow of current over said circuit connection above a predetermined value heating the semi-conducting member sufficient to cause collapse thereof by the pressure of said contact element thereby releasing said contact element for movement into said aperture by action of said spring, positioning of the contact element in the aperture electrically separating the contact element from the conductor whereby said circuit connection is broken.

2. A device according to claim 1, and further comprising an insulation plate mounting the other end of said spring, said conductor forming an open casing secured with its open side to said plate.

3. A device according to claim 1, wherein said contact element has a blank end face abutting against said semiconducting member and an insulated side wall for insulating the contact element from said conductor upon penetration of the contact element into said conductor aperture due to a collapse of the semi-conducting member and the resulting movement of the contact element toward the conductor, thereby interrupting said circuit connection.

4. A device according to claim 1, wherein said contact element has a blank end face abutting against said semi conducting member and an insulated side wall for insulating the contact element from said conductor upon movement of the contact element into said conductor aperture due to a collapse of the semi-conducting memher and the resulting movement of the contact element toward the conductor, and wherein a second conductor is disposed opposite the other side of the first conductor electrically insulated therefrom, the blank face of said contact element engaging said second conductor due to its aforesaid movement upon collapse of the semi-conducting member thereby electrically connecting said spring and said second conductor through said contact element.

5. A device according to claim 4, wherein the said spring is a leaf spring fixedly held on one end and supporting said contact element.

6. A device according to claim 1, and further comprising a switch means having a springy switch contact biased into its switch opening position, said spring mounting the contact element holding said switch contact in its switch closing position by abutment of said contact element against said semi-conducting member, collapse of said semi-conducting member and the resulting movement of the contact element into the conductor aperture releasing the switch contact for opening of said switch means.

7. A control device for supervising a plurality of switching means in an automatic telephone exchange, said device comprising a metal spring for each switching means to be supervised, a common insulator mounting all said springs, each of said springs supporting a contact element, a common conductor disposed opposite said contact elements and formed with holes, each of said holes being situated in alignment with a respective one of said contact elements, a common semi-conductor disposed between said contact elements and said common conductor in conductive contact with said contact elements and said conductor, the material of said semi-conductor having a materially reduced'breakiug strength when heated, each of said springs being biased to press the respective contact element against a portion of the semi-conductor, each of said springs and contact elements, said common semi-conductor and said common conductor constituting a supervising circuit including a respectiveone of said switching means to be supervised, a current flow in any one of said circuits heating the portion of the semi-conductor engaged by the respective contact element sufiicient to cause collapse of the said portion by the pressure of the said contact element and releasing the respective contact element in movement into the respective hole of the common conductor, the said movement being indicative of an actuation of the switching means included in the respective supervising circuit.

8. A control device according to claim 7 wherein said common semi-conductor is removably mounted for readily exchanging the same for inspection.

9. A control device according to claim 7 wherein said common semi-conductor is made of compressed paper pulp mixed with charcoal particles.

References Cited in the file of this patent UNITED STATES PATENTS 684,007 Stromberg Oct. 8, 1901 817,959 Craft Apr. 17, 1906 1,857,322 Nordhem May 10, 1932 2,179,935 Kayatt Nov. 14, 1939 

